High-pressure pump

ABSTRACT

Between a movable core chamber and a fuel supply passage, a needle guide slidably supports a needle fixed to a movable core. The needle guide has a communication hole which fluidly connects the movable core chamber and the fuel supply passage. An opening sectional area of the communication hole is defined in such a manner that a fuel discharged amount decreases as an energization start time of a coil is delayed. In a suction stroke, it is restricted that the movable core and the needle bounce toward the fixed core after the needle biases a suction valve toward a stopper by means of a biasing force of a second spring. A relationship between the energization start time of the coil and the fuel discharged amount is properly maintained, so that the fuel discharged amount of the high-pressure pump can be controlled correctly.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of Ser. No. 13/933,450, filed Jul. 2, 2013, whichis based on Japanese Patent Applications No. 2012-150697 filed on Jul.4, 2012, and No. 2013-063987 filed on Mar. 26, 2013, the disclosures ofeach of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a high-pressure pump.

BACKGROUND

A fuel supply system which supplies fuel to an engine is equipped with ahigh-pressure pump which pressurizes the fuel suctioned from a fueltank. A high-pressure pump has a plunger which pressurizes the fuelintroduced into a pump chamber through a fuel inlet and a fuel supplypassage. The pressurized fuel is discharged through a fuel outlet.

JP-2001-304068A shows a high-pressure pump having a needle valve fixedto a movable core. The needle valve sits on or moves apart from a valveseat to close or open the fuel supply passage. The needle valve issupported by a needle guide which is arranged between a movable corechamber and the fuel supply passage. The needle guide has acommunication hole which fluidly connects the movable core chamber andthe fuel supply passage. Thereby, a movable core chamber functions as adamper chamber, so that a noise due to a collision between the needlevalve and the valve seat can be reduced.

In the above high-pressure pump, as an opening sectional area of thecommunication hole is made larger, a flow resistance of the fuel flowingthrough the communication hole becomes smaller and the operation and amovement of the movable core become quicker.

Thus, in a suction stroke of the high-pressure pump, after the movablecore and the needle valve collide with a stopper by a biasing force of aspring, it is likely that the movable core and the needle valve maybounce toward a fixed core. At this moment, when the movable core andthe needle valve are magnetically attracted to the fixed core in ametering stroke, a valve-close time of the needle valve is made earlier,so that a discharging stroke starts earlier than an intended time. Evenif an energization start time of a coil is made later, the fueldischarge quantity is increased. It may be difficult to control the fueldischarge quantity with high accuracy.

SUMMARY

It is an object of the present disclosure to provide a high-pressurepump capable of controlling its fuel discharge quantity with highaccuracy.

According to a high-pressure pump of the present disclosure, a movablecore chamber and a fuel supply passage are defined by a needle guide.The needle guide has a communication hole fluidly connecting the movablecore chamber with the fuel supply passage. An opening sectional area ofthe communication hole is defined so that a fuel discharged amountdecreases as an energization start time of the coil is delayed.

A fuel flow from the fuel supply passage to the movable core chamber isadjusted according to the opening sectional area of the communicationhole, so that an operation of the movable core can be controlled.Thereby, in the suction stroke, it is restricted that the movable coreand the needle bounce toward the fixed core after the needle biases thesuction valve toward stopper by means of a biasing force of a biasingportion. Therefore, the relationship between the energization start timeof the coil and the fuel discharged amount is properly maintained. Thefuel discharged amount of the high-pressure pump can be controlledcorrectly.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a cross-sectional view showing a high-pressure pump accordingto a first embodiment;

FIG. 2 is an enlarged view of an essential part of FIG. 1;

FIG. 3 is an enlarged view of an essential part of FIG. 2;

FIGS. 4A to 4D are graphs showing analytical data of stress condition ofa gap between a movable core and a fixed core;

FIG. 5 is a graph showing a relationship between a bubble collapsestrength and a final gap amount between the movable core and the fixedcore;

FIG. 6 is a graph showing a relationship between a cross-sectional areaof a communication hole and the bubble collapse strength in the finalgap;

FIGS. 7A and 7B are photographs respectively showing a condition of asurface of the movable core;

FIG. 8 is a graph showing frequency characteristics of sound generatedfrom a solenoid valve of the first embodiment and a solenoid valve of acomparative example;

FIG. 9 is a graph showing a sound pressure level of a time when asolenoid valve is energized, according to a comparative example;

FIG. 10 is a graph showing a sound pressure level of a time when asolenoid valve is energized, according to the first embodiment;

FIG. 11 is a graph showing frequency characteristics in a collisionregion of a solenoid valve of the first embodiment and a solenoid valveof a comparative example;

FIG. 12 is a graph showing frequency characteristics in an attenuationregion of a solenoid valve of the first embodiment and a solenoid valveof a comparative example;

FIG. 13 is a graph showing noise frequency characteristics of when thecross-sectional area of the communication hole is varied in thehigh-pressure pump of the first embodiment.

FIG. 14 is a graph showing overall values of 0 to 10 kHz of when thecross-sectional area of the communication hole is varied in thehigh-pressure pump of the first embodiment.

FIG. 15 is a cross-sectional view showing an essential part of ahigh-pressure pump according to a comparative example;

FIG. 16 is a cross-sectional view showing an essential part of ahigh-pressure pump according to a second embodiment;

FIG. 17 is a graph showing a relationship between an energization starttime of a solenoid valve and a fuel discharge amount of a high-pressurepump;

FIG. 18 is an enlarged view of part XVIII in FIG. 17;

FIGS. 19A to 19C are charts showing a relationship between an innerdiameter of a communication hole and a behavior of a needle; and

FIG. 20 is a graph showing a relationship between an opening sectionalarea of a communication hole and a valve-close-response time of asuction valve.

DETAILED DESCRIPTION

Multiple embodiments will be described with reference to accompanyingdrawings.

First Embodiment

Referring to FIGS. 1 to 14, a first embodiment will be described. Ahigh-pressure pump 1 is provided to a fuel-supply system which suppliesfuel to an internal combustion engine. The fuel pumped up from a fueltank is pressurized by the high-pressure pump 1. The pressurized fuel isaccumulated in a delivery pipe. Then, the high-pressure fuel accumulatedin the delivery pipe is injected into each cylinder of the enginethrough a fuel injector.

(Configuration of High-Pressure Pump and Electromagnetic Valve)

As shown in FIG. 1, the high pressure pump 1 is provided with a pumpbody 40, a plunger 42, a damper chamber 50, a solenoid valve 10, and adischarge valve 60. The pump body 40 forms a cylinder 41 therein. Thecylinder 41 receives the plunger 42 reciprocatably. A spring 46 isarranged between a spring seat 43 and an oil-seal holder 45. The springseat 43 is disposed to a tip end of the plunger 42. The oil-seal holder45 holds an oil seal 44 on an outer circumference of the plunger 42. Thespring 46 biases the plunger 42 toward a camshaft (not shown) of theengine. The plunger 42 reciprocates in its axial direction according toa cam profile of the camshaft. When the plunger 42 reciprocates, avolume of the pump chamber 47 varies, so that the fuel is introducedinto the pump 47 and is pressurized therein.

Next, the damper chamber 50 will be described in detail.

The pump body 40 has a cylindrical portion 51 protruding opposite to thecylinder 41. A cover 52 is provided on the cylindrical portion 51 todefine the damper chamber 50. The damper chamber 50 accommodates apulsation damper 53, a supporting member 54, and a wavy spring 55. Thepulsation damper 53 is comprised of two metallic diaphragms in which airof specified pressure is sealed. The pulsation damper 53 reduces fuelpressure pulsation in the damper chamber 50.

The damper chamber 50 communicates with a fuel inlet (not shown) througha fuel passage (not shown). The fuel in a fuel tank (not shown) issupplied to the fuel inlet. The fuel in the fuel tank is introduced intothe damper chamber 50 through the fuel inlet.

Next, the solenoid valve 10 will be described in detail.

As shown in FIGS. 2 and 3, the solenoid valve 10 is disposed in a fuelsupply passage 48 which connects the pump chamber 47 and the damperchamber 50. The fuel supply passage 48 is opened or closed by thesolenoid valve 10. The solenoid valve 10 is provided with a fixed core11, a movable core 12, a coil 13, a second spring 14, a core housing 15and a needle guide 16.

The pump body 40 has a small-diameter portion 49 which extendsperpendicularly relative to a center line of the cylinder 41. An openingof the small-diameter portion 49 is covered with the core housing 15,whereby the fuel supply passage 48 is defined from the damper chamber 50to a pump chamber 47.

A stopper 17, a seat member 18, and a cylinder member 19 are arranged inthe fuel supply passage 48 in this order. The stopper 17 is cup-shapedto accommodate a suction valve 20 therein. The suction valve 20reciprocates in the cup-shaped stopper 17 and the stopper 17 regulates amovement of the suction valve 20 in a valve-open direction. A firstspring 21 is provided between the stopper 17 and the suction valve 20.The first spring 21 biases the suction valve 20 in a valve-closingdirection. The stopper 17 has an aperture 22 through which the fuelflows.

The seat member 18 has an annular valve seat 23 on which the suctionvalve 20 can sit. When the suction valve 20 sits on the valve seat 23,the fuel supply passage 48 is closed. When the suction valve 20 movesapart from the valve seat 23, the fuel supply passage 48 is opened. Thecylinder member 19 is threaded to a female screw 481 formed on an innerwall of the fuel supply passage 48. Thereby, the stopper 17, the seatmember 18 and the cylinder member 19 are fixed in fuel supply passage48.

The needle guide 16 is fixed inside of the core housing 15. The needleguide 16 separates a movable core chamber 24 from the fuel supplypassage 48. The movable core 12 is accommodated in the movable corechamber 24. The needle guide 16 has a communication hole 25 whichfluidly connects the movable core chamber 24 and the fuel supply passage48. The communication hole 25 is comprised of a large-diameter hole 251and a small-diameter hole 252. The large-diameter hole 251 confronts tothe movable core chamber 24. The small-diameter hole 252 confronts tothe fuel supply passage 48. According to the first embodiment, an innerdiameter of the small-diameter hole 252 is 1.2 mm or less. Preferably,the inner diameter is 1.0 mm or less. That is, an opening sectional areaof the small-diameter hole 252 is 0.36 πmm² or less. Preferably, theopening sectional area is 0.25 πmm² or less. The needle guide 16supports the needle 26 slidably in its axial direction.

One end of the needle 26 is connected to the movable core 12 and theother end can be in contact with the suction valve 20. The needle 26 hasan enlarged portion 27 of which outer diameter is larger than that ofthe other portion. When the needle 26 moves toward the fixed core, theenlarged portion 27 is brought into contact with the needle guide 16.Moreover, the needle 26 has a flange 28. A second spring 22 is providedbetween the flange 28 and the needle guide 16. The second spring 14biases the needle 26 with a biasing force which is greater than that ofthe first spring 21. That is, the second spring 14 biases the movablecore 12 in such a manner as to be apart from the fixed core 11.

The movable core 12 is made from magnetic material and is accommodatedin the movable core chamber 24 which is defined in the core housing 15.The movable core 12 axially reciprocates in the movable core chamber 24.The movable core 12 has multiple breathing ports 29 which extend in itsaxial direction. In the first embodiment, an outer diameter of themovable core 12 is 9.7 mm. An outer diameter of the needle 26 is 3.0 mm.It should be noted that the outer diameters of the movable core 12 andthe needle 26 are established based on various factors, such as magneticattraction force or capacity of the high-pressure pump.

The fixed core 11 is made from magnetic material. A ring portion 111 issandwiched between the fixed core 11 and the core housing 15. When theneedle 26 moves toward the fixed core 11 and the enlarged portion 27 isbrought into contact with the needle guide 16, a small space is definedbetween the fixed core 11 and the movable core 12. This small space isreferred to as a final gap.

In first embodiment, when the final gap is defined, a distance betweenthe fixed core 11 and the movable core 12 is 0.08-0.16 mm. That is, whenthe outer diameter of the movable core 12 is 9.7 mm, the volume of afinal gap is 1.8818 πmm³ to 3.7636 πmm³.

A connector 30 is provided to the fixed core 11. The connector 30 issupported by a cylindrical yoke 31. The yoke 31 is fixed to the corehousing 15. A coil 13 is wound around a bobbin 32. When the coil 13 isenergized through a terminal 33 of the connector 30, the coil 13generates a magnetic field.

When the coil 13 is not energized, the movable core 12 and the fixedcore 11 are apart from each other due to the biasing force of the secondspring 14. The needle 26 moves toward the pump chamber 47 and the needle38 pushes the suction valve 20, whereby the suction valve 20 is opened.When the coil 13 is energized, a magnetic flux is generated in themagnetic circuit formed by the fixed core 11, the movable core 12, theyoke 31 and the core housing 15. The movable core 12 is magneticallyattracted toward the fixed core 11 against the biasing force of thesecond spring 14. Consequently, the needle 26 relieves a pressing forceagainst the suction valve 20.

Then, the discharge valve 60 will be described hereinafter.

The discharge valve 60 is comprised of a discharge valve body 61, aregulation member 62 and a spring 63. The pump body 40 defines adischarge passage 64 which extends perpendicularly relative to thecenter axis of the cylinder 41. The discharge valve body 61 is slidablyaccommodated in the discharge passage 64. The discharge valve body 61sits on the valve seat 65 to close the discharge passage 64 and movesaway from the valve seat 65 to open the discharge passage 64. Theregulation member 62 regulates a movement of the discharge valve body 61toward a fuel outlet port 66. One end of the spring 63 is engaged withthe regulation member 62 and the other end is engaged with the dischargevalve body 61. The spring 63 biases the discharge valve body 61 towardthe valve seat.

When the fuel pressure in the pump chamber 47 is increased and thedischarge valve body 61 receives a force greater than a total of thebiasing force of the spring 63 and the fuel pressure downstream of thevalve seat 65, the discharge valve body 61 moves away from the valveseat 65. The fuel is discharged through the fuel outlet port 66.

Meanwhile, when the fuel pressure in the pump chamber 47 is decreasedand the discharge valve body 61 receives a force smaller than the totalof the biasing force of the spring 63 and the fuel pressure downstreamof the valve seat 65, the discharge valve body 61 sits on the valve seat65. Thereby, a reverse flow of the fuel from the valve seat 65 towardthe pump chamber 47 is avoided.

(Operation of High-Pressure Pump)

An operation of the high-pressure pump 1 will be described hereinafter.In the following description, a time-lag from when the coil 13 isenergized until when the movable core 12, the needle 26 or the suctionvalve 20 moves is not considered.

(1) Suction Stroke

When the plunger 42 slides down from a top dead center toward a bottomdead center, the volume of the pump chamber 47 is increased. Thedischarge valve body 61 sits on the valve seat 65 to close the dischargepassage 64.

Meanwhile, the suction valve 20 receives a differential pressure betweenthe pump chamber 47 and the fuel supply passage 48, whereby the suctionvalve 20 moves toward the pump chamber 47 against the biasing force ofthe first spring 21. The suction valve 20 is opened. At this time, sincethe coil 13 has been deenergized, the movable core 12 and the needle 26are moved toward the pump chamber 14 by the biasing force of the secondspring 14. The movable core 12 and the needle 26 bias the suction valve20 toward the pump chamber 47. Thus, the suction valve 20 is keptopened. The fuel is suctioned into the pump chamber 47 from the dumperchamber 50 through the fuel supply passage 48.

(2) Metering Stroke

When the plunger 42 slides up from the bottom dead center to the topdead center along with a rotation of the cam shaft, the volumetriccapacity of the pump chamber 47 is reduced. At this moment, since thecoil 13 has been deenergized, the needle 26 and the suction valve 20 arepositioned at the open position by a biasing force of the second spring14. The fuel supply passage 48 is kept opened. Thus, the fuel in thepump chamber 47 is returned to the dumper chamber 50 through the fuelsupply passage 48. The pressure in the pump chamber 47 does notincrease.

(3) Pressurization Stroke

While the plunger 42 slides up from the bottom dead center to the topdead center, the coil 13 is energized. The coil 13 generates a magneticfield and a magnetic attraction force is generated between the fixedcore 11 and the movable core 12. When the magnetic attraction forcebecomes greater than a difference between the biasing force of thesecond spring 14 and the biasing force of the first spring 21, themovable core 12 and the needle 26 move toward the fixed core 11.Thereby, a pushing force of the needle 26 to the suction valve 20 iscanceled. The first spring 21 and the low-pressure fuel discharged fromthe pump chamber 47 bias the suction valve 20 toward the valve seat 23.The suction valve 20 sits on the valve seat 23 to close the fuel supplypassage 48.

After the suction valve 20 sits on the valve seat 23, the fuel pressurein the pump chamber 47 increases while the plunger 42 slides up to thetop dead center. When the fuel pressure applied to the discharge valvebody 61 in the pump chamber 47 becomes greater than a total of the fuelpressure applied to the discharge valve body 61 in the discharge passage64 and the biasing force of the spring 63, the discharge valve body 61is opened. Thereby, the high-pressure fuel pressurized in the pumpchamber 47 is discharged to the fuel outlet port 66 through thedischarge passage 64.

It should be noted that the energization of the coil 13 is stopped inthe pressurization stroke. Since the fuel pressure applied to thesuction valve 20 in the pump chamber 47 is greater than the biasingforce of the second spring 14, the suction valve 20 is kept closed.

The high-pressure pump 1 repeats the above strokes (1) to (3) topressurize and discharge the fuel which the internal combustion enginerequires.

(Reduction of Erosion)

A stress condition in the final gap between the fixed core 11 and themovable core 12 will be explained. The stress condition represents acondition of an end surface of the movable core 12 confronting to thefixed core 11 or an end surface of the fixed core 11 confronting to themovable core 12. These end surfaces receive stresses of erosiongenerated by cavitation. As bubble collapse strength of the cavitationis larger, the stress is greater.

The bubble collapse strength is expressed by a product of a voidfraction and a force which crushes the bubble. The void fraction is arate of the amount of bubbles relative to the volume of the gap. Thebubble crushing force is expressed by fluid acceleration.(Bubble collapse strength)=(Void fraction (%))×(Fluid acceleration(mm/s²))

As a pressure fluctuation is the gap between the fixed core 11 and themovable core 12 becomes larger, the amount of bubbles is more increased.The pressure fluctuation in the gap is expressed by a following formula(1).ΔP=(ΔV/Vo)×E  (1)

ΔP: Pressure fluctuation in the gap

ΔV: Absolute value of the variation of the volume of a gap at a timewhen the movable core moves to the fixed core

Vo: Volume of the gap at a time when the movable core is most apart fromthe fixed core

E: Bulk modulus of the liquid flowing into the gap

As the pressure fluctuation ΔP becomes larger, the amount of bubbles inthe gap is more increased.

FIG. 15 shows a comparative example of a high-pressure pump 2. Thehigh-pressure pump 2 is a “solid gap type” pump in which the fixed core11 and the movable core 12 are brought into contact with each other whenthe coil 13 is energized. In the following description about thecomparative example of the high-pressure pump 2, the substantially sameparts and the components as those in the first embodiment are indicatedwith the same reference numeral and the same description will not bereiterated.

In the high-pressure pump 2, the suction valve 20 and the needle 26 areindependently provided in the valve body 3. Unlike the first embodiment,the needle 26 has no enlarged portion. Thus, in the high-pressure pump2, when the coil 13 is energized, the fixed core 11 and the movable core12 are brought into contact with each other. The pressure fluctuation ina portion between the fixed core 11 and the movable core 12 becomeslarger. The void fraction is increased and the bubble collapse strengthbecomes larger. As a result, the stress applied to the end surfaces ofthe movable core 12 and the fixed core 11 becomes larger.

On the other hand, according to the first embodiment, the solenoid valve10 is an “air gap type” valve in which the movable core 12 is notbrought into contact with the fixed core 11. Thus, the pressurefluctuation between the fixed core 11 and the movable core 12 becomessmaller. The void fraction is reduced and the bubble collapse strengthbecomes smaller.

Referring to analytical data shown in FIGS. 4A to 4D, the stresscondition in the gap between the movable core 12 and the fixed core 11of the solenoid valve 10 of the first embodiment will be described.

FIG. 4A shows a behavior of the needle 26. It should be noted that theneedle 26 and the movable core 12 moves together according to the firstembodiment. After the cam angle passes 270 (deg), the movable core 12magnetically attracted toward the fixed core 11 and the needle 26 isalso attracted toward the fixed core 11. The enlarged portion 27 and theneedle guide 16 are brought into contact with each other when the camangle is 290 (deg). The needle 26 comes most close to the fixed core 11.Then, while the cam angle is 310 to 330 (deg), the coil 13 isdeenergized, so that the needle 26 slightly moves toward the pumpchamber 47. While the cam angle is 330 to 350 (deg), the suction valve20 moves apart from the valve seat 23 and the needle 26 moves toward thepump chamber along with the suction valve 20.

FIG. 4B shows the void fraction in the gap between the movable core 12and the fixed core 11. While the cam angle is 290 to 350 (deg) and theneedle 26 moves toward the fixed core 11, the void fractionsignificantly varies. An increase and a decrease are repeated.

FIG. 4C shows the fluid acceleration of the fuel flowing through thebreathing ports 29 of the movable core 12. When the needle 26 comes mostclose to the fixed core 11 at the cam angle of 290 (deg), the fluidacceleration becomes large. Also, while the coil 13 is deenergized atthe cam angle of 310 to 330 (deg), the fluid acceleration becomes large.

FIG. 4D shows the bubble collapse strength in the gap between themovable core 12 and the fixed core 11. The bubble collapse strengthbecomes the largest value when both the void fraction and the fluidacceleration become large at the cam angle of 290 (deg). Also, when boththe void fraction and the fluid acceleration become large at the camangle of 310 to 330 (deg), the bubble collapse strength becomes large.

From the above analytical data shown in FIGS. 4A to 4D, it is apparentthat the bubble collapse strength in the gap between the movable core 12and the fixed core 11 is largest when both of the void fraction and thefluid acceleration became large.

Referring to the analytical data shown in FIG. 5, a relationship betweena final gap amount and the bubble collapse strength in the final gapwill be explained.

In a case that a target value of the bubble collapse strength is set to200 or less, the target value can be obtained when the final gap amountis 0.8 mm or more. However, when the final gap amount is 0.16 mm ormore, it is likely that the magnetic attraction force between themovable core 12 and the fixed core 13 may be decreased. Therefore, thefinal gap amount is established at the value of 0.08 to 0.16 mm. Whenthe outer diameter of the movable core 12 is 9.7 mm, the volume of thefinal gap is 1.8818 πmm³ to 3.7636 πmm³.

Referring to the analytical data shown in FIG. 6, a relationship betweena cross-sectional area of the communication hole 25 and the bubblecollapse strength in the final gap will be explained.

A solid line “A” in FIG. 6 shows a case where the movable core 12 hasfour breathing ports 29. An inner diameter of each breathing port 29 is1 mm and a total cross area of the breathing ports 29 is about 3.14 mm².A solid line “B” in FIG. 6 shows a case where the movable core 12 hassix breathing ports 29. An inner diameter of each breathing port 29 is 1mm and a total cross area of the breathing ports 29 is about 4.71 mm².

In a case that a target value of the bubble collapse strength isestablished less than 200, the target value can be obtained when a totalcross-sectional area of the breathing ports 29 is about 4.71 mm², and across-sectional area of the communication hole 25 is 0.36 πmm² (about1.13 mm²) or less. When the cross-sectional area of the communicationhole 25 is 0.36 πmm², the needle guide 16 has only one communicationhole 25 of which inner diameter is 1.2 mm or less.

Meanwhile, when the cross-sectional area of the breathing ports 29 ismade larger, the bubble collapse strength became smaller. However, thiseffect is smaller than a case in which the cross-sectional area of thecommunication hole 25 is varied.

FIGS. 7A and 7B respectively show the condition of the end surface ofthe movable core 12 after the high-pressure pump 1 has been driven for aspecified time period.

FIG. 7A shows the condition of a case in which the needle guide 16 hasone communication hole 25 of which inner diameter is 1.2 mm.

FIG. 7B shows the condition of a case in which the needle guide 16 hasthree communication holes 25 of which inner diameter is 1.2 mm.

This experiment is conducted under the following conditions:

Fuel pressure: 20 MPa,

Fuel: Gasoline,

Cam mountain: Four cam mountains of 4 mm height,

Engine speed: 3500 rpm,

Discharge amount of High-pressure-pump: Full discharge,

Experiment Time: 180 H (3.7×10⁸ times),

Final gap: 0.1 mm,

Breathing port: Six breathing ports (4.71 mm²)

According to the above experimental result, it becomes apparent that theerosion at the end surface of the fixed core 11 is more restricted whenthe cross-sectional area of the communication hole 25 of a needle guide16 is made smaller.

(Reduction of Noise Vibration)

A noise vibration of the high-pressure pump will be described,hereinafter.

FIG. 8 is a graph showing frequency characteristics of noise generatedby the high-pressure pump of the first embodiment and the high-pressurepump of the comparative example. As above-mentioned, the high-pressurepump of the first embodiment is an “air gap type”, and the high-pressurepump of a comparative example is a “solid gap type.” According to thefirst embodiment, as shown in FIGS. 8 and 10 to 13, the high-pressurepump 1 has three communication holes 25 of which inner diameter is 1.2nm.

Meanwhile, the high-pressure pump of the comparative example shown inFIG. 15 has a solenoid valve.

A dashed line “C” in FIG. 8 shows the frequency characteristics of thenoise generated by the high-pressure pump of the first embodiment. Asolid line “D” shows the frequency characteristics of the noisegenerated by the high-pressure pump of the comparative example.

In the high-pressure pump of the first embodiment, the noise of whichfrequency is around 3 to 5 kHz and 7 to 9 kHz is high.

FIG. 9 is a graph showing a sound pressure level ofsuction-valve-closing noise generated when the coil is energized in thehigh-pressure pump of the comparative example. FIG. 10 is a graphshowing a sound pressure level of suction-valve-closing noise generatedwhen the coil is energized in the high-pressure pump of the firstembodiment. The sound pressure level of the comparative example isquickly attenuated as shown by an arrow “E” in FIG. 9. Meanwhile, thesound pressure level of the first embodiment is slowly attenuated asshown by an arrow “F” in FIG. 10.

The frequency characteristics in a collision region (0.010 to 0.012 sec)of FIGS. 9 and 10 are shown in FIG. 11. A dashed line “G” shows thefrequency characteristics in the collision region of the firstembodiment. A solid line “H” shows the frequency characteristics in thecollision region of the comparative example. As a result, there is nosignificant difference in frequency characteristics in the collisionregion between the comparative example and the first embodiment.

The frequency characteristics in an attenuation region (0.012 to 0.018sec) of FIGS. 9 and 10 are shown in FIG. 12. A dashed line “I” shows thefrequency characteristics in the attenuation region of the firstembodiment. A solid line “J” shows the frequency characteristics in theattenuation region of the comparative example. As the result, in thehigh-pressure pump of the first embodiment, the noise of which frequencyis around 3 to 5 kHz and 7 to 9 kHz is high. The deterioration infrequency characteristics of the high-pressure pump of the firstembodiment, which is shown in FIG. 8, is caused due to a deteriorationin frequency characteristics of valve-close noise of the suction valvein the attenuation region (0.012 to 0.018 sec).

FIG. 13 is a graph showing noise frequency characteristics of when thecross-sectional area of the communication hole 25 of the needle guide 16is varied in the high-pressure pump of the first embodiment. A dashedline “K” in FIG. 13 represents the frequency characteristics ofvalve-close noise in the attenuation region (0.012 to 0.018 sec) in acase where the needle guide 16 has three communication holes 25 of whichinner diameter is 1.2 mm. The dashed line “K” in FIG. 13 is identical tothe dashed line “I” in FIG. 12. A solid line “L” in FIG. 13 representsthe frequency characteristics of valve-close noise in the attenuationregion (0.012 to 0.018 sec) in a case where the needle guide 16 has onlyone communication hole 25 of which inner diameter is 1.2 mm. As aresult, it becomes apparent that the noise of which frequency is about 3to 5 kHz and 6 to 9 kHz is reduced in a case that the needle guide 16has only one communication hole 25 of which inner diameter is 1.2 mm.

FIG. 14 is a chart showing overall values of the noise vibration ofwhich frequency is 0 to 10 kHz. The noise vibration is generated when across-sectional area of the communication hole 25 is varied in a casethat the needle guide 16 has only one communication hole 25.

In a case that a target value of the overall value of noise vibration isset as “T”, the overall value can be made lower than or equal to “T”when the needle guide 16 has only one communication hole 25 of whichinner diameter is 1.2 mm. Preferably, when the needle guide 16 has onlyone communication hole 25 of which inner diameter is 1.0 mm or less, theoverall value of the noise vibration can be further decreased.

Advantages of the First Embodiment

According to the above first embodiment, following functional advantagescan be achieved.

(1) The opening sectional area of the communication hole 25 is definedin such a manner as to reduce an erosion on an end surface of themovable core 12 or the fixed core 11. Specifically, the openingsectional area of the communication hole 25 is larger than zero and isless than or equal to 0.36 πmm². That is, the opening sectional area ofthe communication hole 25 is larger than 0% and less than or equal to1.69% relative to a cross sectional area which is obtained bysubtracting the cross-sectional area of the needle 26 from thecross-sectional area of the movable core 12.

According to the above configuration, a fluid acceleration of the fuelflowing into the movable core chamber 2 through the fuel supply passage48 and the communication hole 25 is reduced. Therefore, the fluidacceleration of the fuel flowing from the movable core chamber 24 intothe gap between the movable core 12 and the fixed core 11 through thebreathing ports 29 is reduced. Since the bubble collapse strength in thegap between the movable core 12 and the fixed core 11 becomes smaller,the erosion on the end surfaces of the movable core 12 and the fixedcore 11 can be restricted. As a result, the deterioration in magneticattraction force between the movable core 12 and the fixed core 11 canbe restricted. The discharging efficiency of the high-pressure pump 1can be maintained.

(2) In the first embodiment, when the movable core 12 is magneticallyattracted toward the fixed core 11, the enlarged portion 27 and theneedle guide 16 are brought into contact with each other and the finalgap is defined between the movable core 12 and the fixed core 11.Thereby, it can be restricted that bubbles in the fuel in the final gapare collapsed.

(3) In the first embodiment, the volume of the final gap between themovable core 12 and the fixed core 11 is established in such a mannerthat the erosion on the end surfaces of the movable core 12 and thefixed core 11 is reduced and the magnetic attraction force between themovable core 12 and the fixed core 11 is maintained. Specifically, whenthe final gap is defined, a distance between the fixed core 11 and themovable core 12 is 0.08-0.16 mm. When the outer diameter of the movablecore 12 is 9.7 mm, the volume of the final gap is 1.8818 πmm³ to 3.7636πmm³. The outer diameter of the movable core 12 is not limited to theabove value.

Thus, the erosion on the end surface of the movable core 12 can berestricted.

(4) A noise vibration is generated due to a contact between the enlargedportion 27 and the needle guide 16 when the coil 13 intermittently isenergized. In the first embodiment, the opening sectional area of thecommunication hole 25 is defined in such a manner that the noisevibration is reduced. Specifically, the opening sectional area of thecommunication hole 25 is 0.36 πmm² or less. Preferably, the openingsectional area is 0.25 πmm² or less. Thereby, the noise of a specifiedfrequency can be reduced. The noise vibration of the solenoid valve 10can be reduced.

(5) In first embodiment, the needle guide 16 has only one communicationhole 25 and its inner diameter is 1.2 mm or less, preferably 1.0 mm orless. Thereby, it can be restricted that the erosion occurs on the endsurfaces of the fixed core 11 and the movable core 12. Also, the noisevibration of the solenoid valve 10 can be reduced.

(6) In first embodiment, the second spring 14 is arranged between theflange 28 of the needle 26 and the needle guide 16.

As the comparative high-pressure pump 2 shown in FIG. 15, in a case thata spring-accommodating chamber 4 is defined between the movable core 12and the fixed core 11 to accommodate the second spring 14 therein, it islikely that an erosion may occur on an inner wall surface of thespring-accommodating chamber 4.

Meanwhile, according to the first embodiment, the second spring 14 isarranged in the fuel supply passage 48, whereby it is avoided that anerosion occurs.

(7) The communication hole 25 is comprised of the large-diameter hole251 and a small-diameter hole 252.

Generally, a precision processing is necessary to form a small-diameterhole, which may increase a manufacturing cost. According to the firstembodiment, since the communication hole 25 is comprised of thelarge-diameter hole 251 and the small-diameter hole 252, a relativelength of the small-diameter hole 252 in the communication hole 25 canbe made smaller. Thus, the manufacturing cost can be reduced.

(8) The large-diameter hole 251 is formed on an end surface confrontingto the movable core chamber 24. The small-diameter hole 252 is formed onthe other end surface confronting to the fuel supply passage 48. Thus,the area of the other end surface on which a valve seat is formed is notreduced excessively, whereby the second spring 14 is certainly broughtinto contact with the needle guide 16. Also, it is avoided that thesecond spring 14 is inclined.

Second Embodiment

Referring to FIGS. 16 to 20, a second embodiment will be described. Inthe second embodiment, the substantially same parts and the componentsas those in the first embodiment are indicated with the same referencenumeral and the same description will not be reiterated.

(Configuration of High-Pressure Pump)

A high-pressure pump is an “air gap type” pump as well as the firstembodiment. In the air gap type pump, the movable core 12 and the fixedcore 11 are not brought into contact with each other. Moreover, an outerdiameter of the movable core 12 is 9.57 mm, and an outer diameter of theneedle 26 is 3.3 mm.

Referring to FIG. 16, configurations of the suction valve 20 and thestopper 17 will be explained in detail.

The suction valve 20 is provided with a valve body 201 and a first guideportion 202. The valve body 201 is disk-shaped and is capable of sittingon or being apart from the valve seat 23 of the seat member 18. Thesuction valve 20 is brought into contact with a contacting portion 171of the stopper 17 at its end surface opposite to the valve seat 23.Accordingly, a movement of the suction valve 20 in a valve-opendirection is restricted.

The first guide portion 202 is cylindrical-shaped and extends from thevalve body 201 in a direction opposite to the valve seat 23. An outerperipheral surface of the first guide portion 202 is slidably in contactwith an inner peripheral surface of the second guide portion 172 of thestopper 17. The first guide portion 202 of the suction valve 20 isguided by the second guide portion 172 of the stopper 17, whereby thesuction valve 20 certainly sits on or moves away from the valve seat 23.

The stopper 17 has the contacting portion 171, the second guide portion172, a fixed portion 173, and the aperture 22. The contacting portion171 of the stopper 17 is ring-shaped and is brought into contact with anend surface of the valve body 201. The second guide portion 172 of thestopper 17 is cylindrical-shaped and extends from the contacting portion171 in a direction opposite to the valve seat 23. The second guideportion 172 is slidably in contact with an outer peripheral surface ofthe first guide portion 202. The fixed portion 173 of the stopper 17radially outwardly extends from the contacting portion 171 to be fixedon an inner wall of the fuel supply passage 48. The fixed portion 173divides the pump chamber 47 into a plunger chamber 121 and a valve seatchamber 122.

The fixed portion 173 of the stopper 17 has multiple apertures 22.Specifically, twelve apertures 22 are circumferentially arranged in thefixed portion 173 to fluidly connect the plunger chamber 121 and thevalve seat chamber 122. The second guide portion 172 of the stopper 17has four axial grooves 70 on its inner wall surface. The four axialgrooves 70 are circumferentially arranged at a regular interval. Thecontacting portion 171 of the stopper 17 has four radial grooves 71circumferentially. The radial grooves 71 fluidly connect the axialgrooves 70 and the apertures 22.

A valve chamber 200 accommodating the first spring 21 is defined betweenthe suction valve 20 and the stopper 17. The pump chamber 47 and thevalve chamber 200 communicate with each other through the radial grooves71, the axial grooves 70 and a clearance between the first guide portion202 and the second guide portion 172.

According to the second embodiment, the radial grooves 71 and the axialgrooves 70 correspond to “a passage fluidly connecting the valve chamberand the pump chamber”. It should be noted that a total passage sectionalarea of the four radial grooves 71 is smaller than an area which isobtained by adding the passage sectional area of four axial grooves 70and the passage sectional area of the clearance between the first guideportion 202 and the second guide portion 172.

Thus, when the suction valve 20 is opened, the flow rate of the fuelflowing between the valve chamber 200 and the pump chamber 47 depends onthe passage sectional area of the four radial grooves 71. In a meteringstroke of the high-pressure pump, the fuel flow into the valve chamber200 is restricted by decreasing the passage sectional area of the radialgrooves 71, whereby an excessive pressure increase in the valve chamber200 is restricted, so that a self-close limit speed can be made higher.It should be noted that the self-close limit speed represents a rotatingspeed of a cam shaft of when the suction valve 20 is closed due to afuel pressure in the valve chamber 200 or a dynamic pressure of the fuelflowing into the fuel supply passage 48 from the pump chamber 47 in themetering stroke of the high-pressure pump.

When the suction valve 20 is closed, the end surface of the valve body201 is apart from the contacting portion 171 of the stopper 17. The flowrate of the fuel flowing into the pump chamber 47 from the valve chamber200 depends on a total area of the passage sectional area of four axialgrooves 70 and the passage sectional area of the clearance between thefirst guide portion 202 and the second guide portion 172. Thus, byincreasing the passage sectional area of four axial grooves 70, the fuelflows into the pump chamber 47 from the valve chamber 200 in a suctionstroke of the high-pressure pump. A suction efficiency of the fuel canbe enhanced without a situation where the fuel in the valve chamber 200becomes fluid resistance. That is, since the suction efficiency of thehigh-pressure pump in the second embodiment is higher than that in thefirst embodiment, a fuel discharged amount can be increased.

(Opening Sectional Area of Communication Hole)

The opening sectional area of the communication hole 25 will beexplained hereinafter.

In the high-pressure pump of the second embodiment, the openingsectional area of the communication hole 25 is defined in such a mannerthat a relationship between an energization period of the coil 13 andthe fuel discharged amount is maintained.

FIG. 17 is a graph showing the relationship between the energizationperiod of the coil 13 and the fuel discharged amount while an innerdiameter of the communication hole 25 is varied. In the followingdescriptions, the inner diameter of the communication hole 25 representsan inner diameter of the small-diameter hole 252.

In FIG. 17, a dashed line “S” shows a case where the inner diameter ofthe communication hole 25 is 0.4 mm, a solid line “T” shows a case wherethe inner diameter of the communication hole 25 is 0.5 mm, a long dashedshort dashed line “U” shows a case where the inner diameter of thecommunication hole 25 is 0.6 mm, and an two-dot chain line “V” shows acase where the inner diameter of the communication hole 25 is 0.9 mm.

Generally, in a high-pressure pump, when a force with which the needle26 pushes the suction valve 26 is canceled in a metering stroke, thesuction valve 20 sits on the valve seat 23 to start the dischargingstroke. Thus, as the energization start time of the coil 13 is delayed,the discharge stroke start time is more delayed so that the fueldischarged amount is decreased. It is preferable that such arelationship is maintained in order to control the fuel dischargedamount of the high-pressure pump.

However, in the cases indicated by the long dashed short dashed line “U”and the two-dot chain line “V”, during an energization period of thecoil 13 from BTDC θ1 to BTDC θ2, as the energization start time of thecoil 13 is delayed, the fuel discharged amount is more increased.

Meanwhile, in the cases indicated by the dashed line “S” and the solidline “T”, as the energization start time of the coil 13 is delayed, thefuel discharged amount is more decreased.

FIG. 18 is an enlarged view of XVIII portion in FIG. 17. FIG. 18 showsonly cases indicated by the two-dot chain line “V” and the dashed line“S”.

During an energization period of the coil 13 from BTDC 70 to BTDC θ1, inboth cases indicated by lines “V” and “S”, as the energization starttime of the coil 13 is delayed, the fuel discharged amount is moredecreased.

During an energization period of the coil 13 from BTDC θ1 to BTDC θ2, inthe case indicated by line “V”, as the energization start time of thecoil 13 is delayed, the fuel discharged amount is not decreased. Thereason of the above will be explained with reference to FIGS. 19A to19C.

FIG. 19A shows a cam lift of the camshaft. FIG. 19B is a time chartshowing an energization period of the coil 13 in a case where the coil13 is energized at BTDC θ2. FIG. 19C is a chart showing a behavior ofthe needle 26 in a case where the coil 13 is energized at BTDC θ2. Asolid line “W” shows the behavior of the needle 26 in a case where theinner diameter of the communication hole 25 is 0.9 mm. A dashed line “X”shows the behavior of the needle 26 in a case where the inner diameterof the communication hole 25 is 0.4 mm.

First, based on the solid line “W”, the behavior of the needle 26 willbe explained. At a time t1, the movable core 12 is magneticallyattracted toward the fixed core 11, and the needle 26 is positionedclose to the fixed core 11. At this time, as shown in FIG. 19A, theplunger 42 slides up along with the cam and the high-pressure pumpstarts the discharging stroke.

When the coil 13 is deenergized at a time t2, the magnetic attractionforce is extinguished. After a time t3, the needle 26 moves toward thepump chamber 47 and is brought into contact with the suction valve 20.It should be noted that a time period from the time t2 to the time t3corresponds to a time delay after the coil 13 is deenergized until theneedle 26 starts moving.

After a time t4, the plunger 42 slides down, so that the pump chamber 47is decompressed. The suction valve 20 and the needle 26 move toward thepump chamber 47. When the inner diameter of the communication hole 25 islarger, the flow resistance of the fuel flowing between the movable corechamber 24 and the fuel supply passage 48 will become smaller. Thus, ina case shown by the solid line “W”, the needle 26 moves toward the pumpchamber 47 at the time t6, and then the needle 26 and the movable core12 bounce toward the fixed core 11. At a time t7, the needle 26 bouncesto a position which is close to a half position of a maximum needle liftquantity. After a time t8, the plunger 42 slides up and a meteringstroke is started. When the coil 13 is energized at BTDC 02, that is, atthe time t5, a magnetic attraction force acts on the movable core 12after a specified time delay. At a time t9, the needle 26 starts movingtoward the fixed core 11. The needle 26 is positioned most close to thefixed core 11 at a time t10. Thereby, a fuel discharging stroke isstarted.

Next, based on the dashed line “X”, the behavior of the needle 26 willbe explained. The needle 26 is positioned most close to the fixed coreside 11 at a time t11. Then, the high-pressure pump starts thedischarging stroke. When the coil 13 is deenergized at the time t2, themagnetic attraction force is extinguished. After the time t3, the needle26 moves toward the pump chamber 47 and is brought into contact with thesuction valve 20. When the pump chamber 47 is decompressed, the suctionvalve 20 and the needle 26 move toward the pump chamber 47. When theinner diameter of the communication hole 25 is smaller, the flowresistance of the fuel flowing between the movable core chamber 24 andthe fuel supply passage 48 will become larger. Thus, in the case shownby the dashed line “X”, a bounce amount of the needle 26, which hasmoved toward the pump chamber 47 at the time t12, is small. The needle26 slightly bounces at the time t13. After that, the needle 26 has beenpositioned in the pump chamber 47. After a time t8, the plunger 42slides up and a metering stroke is started. When the coil 13 isenergized at BTDC 02, that is, at the time t5, a magnetic attractionforce acts on the movable core 12 after a specified time delay. Afterthe time t14, the needle 26 starts moving toward the fixed core 11. Atthe time t15, the needle 26 is positioned most close to the fixed core11. Thereby, a fuel discharging stroke is started.

As explained above with reference to FIG. 19, in a case where the innerdiameter of the communication hole 25 is 0.9 mm, the needle 26 which hasmoved to the pump chamber 47 makes a large bounce with the movable core12. Therefore, when the coil 13 is energized at BTDC θ2, the magneticattraction force acts on the movable core 12 after a specified timedelay. While the needle 26 is bouncing, the needle 26 starts movingtoward the fixed core 11. A start time of the fuel discharging stroke ismade earlier than intended, whereby the fuel discharged amount isincreased.

Meanwhile, in a case that the inner diameter of the communication hole25 is 0.4 mm, the needle 26 which has moved toward the pump chamber 47slightly bounces and then the needle 26 is positioned most close to thepump chamber 47. When the coil 13 is energized at BTDC θ2 and themagnetic attraction force acts on the movable core 12, the needle 26starts moving from the pump chamber 47 toward the fixed core 11.Therefore, since the fuel discharging stroke is started at normal time,the fuel discharged amount is not increased.

FIG. 20 is a graph showing a relationship between the opening sectionalarea (mm²) of the communication hole 25 and a valve-close-response time(ms) of the suction valve 20.

When the opening sectional area of the communication hole 25 is madesmaller, the flow resistance of the fuel flowing between the movablecore chamber 24 and the fuel supply passage 48 becomes larger. Thus, atime delay between the coil energization and the needle moving becomeslarger.

When the rotating speed of a cam shaft is 4000 rpm and thevalve-close-response time becomes greater than or equal to 2.2 ms, itwill become difficult to control of the fuel pump. Moreover, if theinner diameter of a communication hole 25 is less than 0.4 mm, it willbecome difficult to form the communication hole 25 by machining.Therefore, the inner diameter of a communication hole 25 is greater thanor equal to 0.4 mm.

Also, as shown in FIG. 17, in a case that the inner diameter of thecommunication hole 25 is less than or equal to 0.5 mm, the fueldischarged amount is more decreased as the energization start time ofthe coil 13 is more delayed. Therefore, it is preferable that the innerdiameter of a communication hole 25 is 0.4 mm to 0.5 mm.

At this time, the opening sectional area of the communication hole 25 is0.20% to 0.31% relative to a cross-sectional area of the movable core 12from which the cross-sectional area of the needle 26 is removed.

According to the above second embodiment, following functionaladvantages can be achieved.

(1) In second embodiment, the inner diameter of the communication hole25 is defined in such a manner that the starting time of the meteringstroke is delayed and the fuel discharged amount is more decreased asthe energization start time of the coil 13 is more delayed.Specifically, the inner diameter of a communication hole 25 is 0.5 mm orless. That is, the opening sectional area of the communication hole 25is 0% to 0.31% relative to the cross-sectional area of the movable core12 from which the cross-sectional area of the needle 26 is removed.

Thereby, in the suction stroke, it is restricted that the movable core12 and the needle 26 bounce toward the fixed core 11 after the needle 26biases the suction valve 20 toward the stopper by means of a biasingforce of the second spring 14. Therefore, the relationship between theenergization start time of the coil 13 and the fuel discharged amount isproperly maintained, so that the fuel discharged amount of thehigh-pressure pump can be controlled correctly.

(2) The opening sectional area of the communication hole 25 is 0.20% ormore relative to the cross-sectional area of the movable core 12 fromwhich the cross-sectional area of the needle 26 is removed. Thereby, thevalve-close-response time of the suction valve 20 becomes shorter, andthe high-pressure pump can be well controlled even when the cam shaftrotates at high speed.

(3) The opening sectional area of the communication hole 25 is 0.4 mm²or more. Thereby, the communication hole 25 of the needle guide 16 canbe formed by machining, so that its manufacturing cost can be reduced.

(4) The pump chamber 47 and the valve chamber 200 communicate with eachother through the radial grooves 71 and the axial grooves 70. Thepassage sectional area of the radial grooves 71 is smaller than thepassage sectional area of the axial grooves 70. Thereby, when thesuction valve 20 starts moving from the valve-close position to thevalve-open position immediately after the suction stroke is started, thefuel flows from the valve chamber 200 to the pump chamber 47 withoutreceiving a flow resistance of the fuel in the valve chamber 200. Avalve open speed of the suction valve 20 is enhanced. As a result, thesuction efficiency of the fuel from the fuel supply passage 48 to thepump chamber 47 can be enhanced.

Meanwhile, in the metering stroke, since the fuel flowing into the valvechamber 200 from a pump chamber 47 is restricted, a fuel pressureincrease in the valve chamber 200 is restricted and the self-close limitspeed can be made higher.

Both the suction efficiency and the self-close limit speed are improved.The fuel discharged amount of the high-pressure pump can be surelycontrolled even when the engine speed is increased and a reciprocatingspeed of the plunger 42 is increased.

Other Embodiment

In the above embodiments, the solenoid valve 10 is a normally openedvalve which is opened when the coil 13 is not energized. Meanwhile, thesolenoid valve 10 may be a normally closed valve which is closed whenthe coil 13 is not energized.

In the above embodiments, the suction valve 20 and the needle 26 areformed independently. Meanwhile, the suction valve 20 and the needle 26may be formed integrally from one piece.

In the second embodiment mentioned above, the radial grooves 71 areformed on the contacting portion 171 of the stopper 17, and the axialgrooves 70 are formed on the second guide portion 172 of the stopper 17.Meanwhile, the radial grooves 71 may be formed on an end surface of thesuction valve, which is opposite to the valve seat. The axial grooves 70may be formed on the first guide portion 202 of a suction valve 20.Moreover, an orifice may be provided at a sliding portion between thefirst guide portion 202 and the second guide portion 172.

The present invention is not limited to the embodiments mentioned above,and can be applied to various embodiments.

What is claimed is:
 1. A high-pressure pump comprising: a plunger; apump chamber in which a fuel is pressurized along with a reciprocationof the plunger; a pump body defining a fuel supply passage through whichthe fuel is supplied to the pump chamber and a discharge passage throughwhich the fuel pressurized in the pump chamber is discharged; a suctionvalve which seals or unseals a valve seat formed on an inner wallsurface of the fuel supply passage so that the pump chamber and the fuelsupply passage are fluidly connected or disconnected with each other; astopper which restricts a movement of the suction valve in a valve-opendirection; a needle which is positioned opposite side of the pumpchamber with respect to the suction valve in such a manner as to biasthe suction valve in the valve-open direction; a movable core which isfixed to an end portion of the needle opposite to the suction valve, themovable core being provided in a movable core chamber in such a manneras to reciprocate in a moving direction of the needle; a fixed corewhich is positioned to an opposite side of the suction valve withrespect to the movable core; a coil which generates a magneticattraction force between the fixed core and the movable core whenenergized; a biasing portion which biases the movable core and theneedle in the valve-open direction of the suction valve; and a needleguide which has a communication hole fluidly connecting the movable corechamber with the fuel supply passage, the needle guide defining themovable core chamber and the fuel supply passage, wherein an openingsectional area of the communication hole is defined so that a fueldischarged amount decreases relative to a maximum fuel discharge amountas an energization start time of the coil is delayed relative to theenergization start time for the maximum fuel discharge amount when abiasing force of the needle to the suction valve is reduced while theplunger slides toward the pump chamber by energizing the coil, wherein:the opening sectional area of the communication hole is greater than 0%and less than or equal to 0.31% of an area which is obtained by removinga cross-sectional area of the needle from a cross-sectional area of themovable core.
 2. A high-pressure pump according to claim 1, wherein: aninner diameter of the communication hole is greater than 0 mm and lessthan or equal to 0.5 mm.
 3. A high-pressure pump according to claim 1,wherein: an inner diameter of the communication hole is greater than orequal to 0.4 mm.
 4. A high-pressure pump according to claim 1, wherein:an inner diameter of the communication hole is 1.00 mm or less andgreater than or equal to 0.4 mm.
 5. A high-pressure pump according toclaim 4, wherein: the passage fluidly connecting the pump chamber andthe valve chamber is comprised of: a radial groove formed on thecontacting portion or the end surface of the valve body in such a manneras to communicate with the pump chamber; and an axial groove formed onthe first guide portion or the second guide portion in such a manner asto fluidly connect the valve chamber with the radial groove.